Squid is a high performance Web proxy cache that can be arranged hierarchically for an improvement in response times and a reduction in bandwith usage. Squid runs on all popular Unix and Windows platforms.

Embedthis Appweb is a fast, little embedded Web server. It is unmatched in efficiency and serves pages at native speed, using an event-driven, non-blocking core to serve multiple requests using minimal resources. It has integrated caching and the ESP "C" Web framework. Without compromising performance, it has extensive security controls and a rigorous security sandbox that helps protect the server and mitigate denial-of-service attacks. It is one of the most widely deployed embedded Web servers and is used in networking equipment, telephony, mobile devices, industrial control, and consumer and office equipment, and in high-performance Web services.

lighttpd is a secure, fast, compliant, and very flexible Web server
which has been optimized for high-performance environments. It has a
very low memory footprint compared to other Web servers, and it takes
care of CPU load. It has an advanced feature set that includes FastCGI
(load balanced), CGI, Auth, Output-Compression, URL-Rewriting, SSL, and
much more.

GNU libmicrohttpd is a small C library for
embedding HTTP server functionality into other
applications. It is reentrant, fast, supports HTTP
1.1, and permits listening on multiple ports. The
API is simple and still powerful enough to allow
programmers to use the entire HTTP feature set.
SSL/TLS support is available as an option.

DeleGate is a multi-purpose application level gateway or proxy server that mediates communication of various protocols, applying cache and conversion for mediated data, controlling access from clients, and routing toward servers. It translates protocols between clients and servers, converting between IPv4 and IPv6, applying SSL (TLS) to arbitrary protocols, merging several servers into a single server view with aliasing and filtering. It can be used as a simple origin server for some protocols (HTTP, FTP, and NNTP).

httping is a "ping"-like tool for HTTP requests. Give it a
URL and it will show how long it takes to connect, send a
request, and retrieve the reply (only the headers). It can
be used for monitoring or statistical purposes (measuring latency).

Pound is a reverse HTTP proxy, load balancer, and SSL wrapper. It proxies client HTTPS requests to HTTP backend servers, distributes the requests among several servers while keeping sessions, supports HTTP/1.1 requests even if the backend server(s) are HTTP/1.0, and sanitizes requests.

MatrixSSL is an embedded SSL and TLS implementation designed for small footprint devices and applications requiring low overhead per connection. The library is less than 50Kb on disk with cipher suites. It includes client and server support through TLS 1.2, mutual authentication, session resumption, and implementations of RSA, ECC, AES, 3DES, ARC4, SHA2, SHA1, and MD5. The source is well documented and contains portability layers for additional operating systems, cipher suites, and cryptography providers.